Who is Miracle Max and Valerie from The Princess Bride and what is their importance?

Miracle Max is King Lotharon's ex-miracle man. William Goldman tells the reader in one of his interruptions that Max was fired by the Prince. This sore spot has rubbed on Max for nearly three years by the time Inigo and Fezzik bring Westley for a cure. Max is excited by the idea of helping to undermine Prince Humperdinck. Max's wife is Valerie. Valerie is not an actual witch but since every miracle man needs a good witch, Valerie learns enough magic to pass herself off as a witch.